DE1667657A1 - Process for the production of wire-shaped silicon carbide crystals and articles consisting entirely or partially of these crystals - Google Patents

Description

Dlpl.-Ing. Erich E. Walther 2000 Hamburg urg 1, 9. Patent attorney Λ Ο α Π CC 7 ^Mftn ^ ^eber 9 ^st

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P 16 67 657 6- ² U File 1 PHN-2074

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"Process for the production of wire-shaped silicon carbide crystals and wholly or partially from these crystals existing objects "

The invention relates to a method for producing wire-shaped silicon carbide crystals and to completely or objects consisting partly of these crystals.

under wire-fed crystals, no more crystals are old here round cross-section also to understand crystals with polygonal, e.g. hexagonal cross-section and ribbon-shaped crystals

Such wire-shaped crystals, which are common in technology as "whiskers" are known to be used to stiffen plastics, glass and metal, for insulation purposes, for pilter and the like.

"Whisker" -like silicon carbide crystals are due to their favorable mechanical properties and chemical resistance even at very high and low temperatures particularly suitable for the purposes mentioned.

Various processes for the production of "whisker" -like silicon carbide crystals have already been described in the literature, label, the yield of the crystals, their dimensions, and their oleic properties varied widely.

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For example, in an atmosphere of hydrogen and nitrogen from a mixture of silicon oxide and carbon at temperatures of 1375 - 1550 ⁰ C, cubic silicon carbide fibers were obtained whose diameter varied from 0.1 to -5 µm and their length from 10 µm to a few centimeters ( British Patent 1,015,844).

It was also described that at temperatures from 1400 to 1600 ° C. from mixtures of a methylehlorsilane and hydrogen or from silicon chloride, hydrocarbon and hydrogen on a graphite substrate a fibrous mass of cubic Silicon carbide was formed, locally some "whisker" -like hexagonal silicon carbide crystals with a thickness of 3 to 10 µm were found, which were up to 1 cm in length. (K.M. Merz, Proc. Conf. Silicon Carbide, Boston 1959, Pp. 73-84, Perganon Press 1960).

It has also already been described (Physical Review rjß (1966) 526), that when a methylchlorosilane is reduced with hydrogen Temperatures of 1350-143O ° C on a graphite substrate crystals of hexagonal «· silicon carbide can be deposited. The number and dimensions of the crystals were given but not in hand. The largest crystals were 3 mm in length and 300 µm in thickness. The smaller whiskers often branched out on common sides of spherical deposits · If locally on the substrate metals, such as Cr, Al, Fe, Co, Cu, Si or Au were attached by precipitation from the vapor phase, an enlargement of the spherical deposits and a reduction in the dimensions of the crystal · obtained «It was found that no growth of silicon carbide crystals in this potash where a so-called vapor-liquid-solid (VLS) mechanism takes place.

Change author (Transaction of Metallurgical Soc. Of A.J.M.E. £ 22 (1965) 1053) “iod, on the other hand, of the opinion that

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"Whisker" growth can probably take place through a VLS mechanism. As is known, this substance is absorbed from a gas phase in a molten drop of a metal forming a solvent for the substance to be crystallized and, after the drop is saturated, is deposited epitaxially on the underlying substrate crystal. A crystal growth proved to be possible for various substances, whereby of course very high demands must be made on the solution with regard to the wetting of the crystal substrate. If the wetting is too low, the contact between the drop and the substrate is insufficient to allow growth over the entire cross-section of the crystal. With good wetting, which can generally be expected with solvents in which the substance to be crystallized dissolves well, the droplet flows out over the sides of the crystal substrate, so that the anisotropic growth required ^{for the formation of "whiskers * 1" does not occur} Can be talked about.

The latter authors have mentioned that by VLS growth when using silicon as a solvent, "whisker" -like Silicon carbide crystals could be obtained.

Experiments which have led to the invention have shown, however, that of the metals which, according to Physical Review 143 »1966, 326, were not considered useful for the VLS growth of" whisker "-like silicon carbide crystals, iron is particularly suitable for this purpose is, while when using this metal even considerably more favorable results in terms of the yield, the dimensions of the crystals and the uniformity of the dimensions were achieved than when using silicon, which has already been proposed as a solvent in this context.

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The fact that in the known method in which locally Elsen was applied to an oracle substrate, no "whisker" growth by a VLS mechanism was found, 1st due to the fact that a graph substrate was used and when a small amount of Elsen is used the crystallization temperature is the whole amount of Elsen in carbide «Was changed and no Elsen very much for a VLS growth remained.

The invention, which is based on the above-described observations and considerations, relates to a method for producing wire-shaped silicon carbide crystals, in which the silicon carbide from an oasis phase containing silicon and carbon grows onto a substrate by a VLS mechanism using a substrate , on the surface of which a solvent for silicon and carbon, which is suitable for the VLS MechaniSBBua, is present in such a font that at elevated temperatures in the gas phase containing silicon and carbon, finely divided droplets are formed from the solvents, SillsiuB and carbon, by means of which Droplets of carbon and silicon from the oasis phase in the form of monocrystalline silicon carbide precipitate at the solid-liquid limit, which is characterized in that iron is used as the solvent and the substrate surface provided with old Elsen at temperatures of at least 1150 ° C, preferably Se over 1200 ⁰ C, but la generally not higher than 1400 ° C, the silicon and carbon-containing oasphase is exposed.

It is not necessary that the Elsen is used in its pure form. Of course, the iron can be used without hesitation already contain carbon or silicon. Other alloying elements can also be present in the iron. Any However, no improvement due to the presence of alloying elements was found.

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In this context, in this description and in the claims, the expression "iron ¹ *" is intended to encompass not only pure iron, but also alloys with bison as the main component, for example types of carbon steel and types of alloy steel.

The iron can be applied to the substrate in various ways for the purpose of obtaining a fine distribution. The substrate surface is preferably cleaned beforehand with Elsen containing powder covered. This can be done, for example, by coating a surface roughened substrate with Elsen, that the substrate is sprinkled with Elsen powder or that Ilsen is applied to the substrate by vapor deposition. In the latter case, the fine distribution is obtained on heating, as a result of which any uniform layer obtained first contracts into separate droplets during the melt formation.

In general, all " material resistant to the temperatures mentioned, wi Graphite, aluminum oxide and silicon carbide. If a substrate such as graphite is used, this will be considerable reacts with iron, if it is of course necessary, that such a large amount of Elsen is applied to the substrate that it is not completely used up before the crystal! sation has started. In individual cases, e.g. thin, vapor-deposited sisenschlchten, e.g. thinner than 1 μ », prove to be unsuitable.

As silicon and carbon-containing oases, alkyl halides, for example methylochlorosilanes, or mixtures of hydrocarbons with silicon tetrahalides or with a halogens such as SiHCl, can be used. In these cases the presence of hydrogen in the oasis phase is necessary to obtain the desired pyrolytic decomposition of the silicon compounds. When using Sl) L ₄ , the • tan easily decomposes and in combination with a carbon

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hydrogen can be applied, the presence of hydrogen is not required. In this Palle one can Inert gas, e.g. argon, can be used as the carrier gas. According to In a preferred embodiment, the silicon and carbon-containing gas phase is produced in a known manner with the help of the cheap starting materials silicon oxide and carbon, preferably in a hydrogen atmosphere.

The crystals obtained consist partly of cubic and partly of hexagonal silicon carbide. If hexagonal If silicon carbide crystals are used as the substrate, a stronger growth of occurs on prism and pyramid surfaces "Whisker" than on base surfaces.

As mentioned above, the "whiskers" can be because of their favorable mechanical properties and chemical resistance can be used for various purposes.

When used for mechanical stiffening of objects, the crystals can be used in materials such as Plastics, glasses and metals, while used as insulation and for filters, e.g. in a die to form plates, blocks and the like.

The silicon carbide crystals according to the invention can not only be used for the purposes mentioned, but they are also particularly suitable for use in building semiconductor devices. The small cross-section of the crystal gives the courtesy of the formation of devices with extremely small dimensions, while also due to the great flexibility of the crystals in their longitudinal direction curved and rolled structures can be formed. When in this application in semiconductor devices In these Crystals PN junctions are required, this can «during

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the growth of the crystals can be achieved by In the oasis phase from which the crystallization takes place, donors and acceptors are doped alternately. Preferred catfish but becomes into the iron used in "whisker" growth a constituent has been added which brings about a certain conductivity type in silicon carbide, while intermittently a different conductivity type over the phase promoting dopant is supplied.

The above items and devices that are totally or consist partly of crystals obtained by the process according to the invention, are also within the scope of the invention.

The invention is explained in more detail below with reference to the drawing and a few examples.

Fig. 1 shows schematically in section an apparatus for performing the method according to the invention.

The device is constructed from a quartz vessel 1 in which a gas atmosphere of the desired composition can be maintained. The quartz vessel 1 is provided with a glass jacket 2 for water cooling.

In the vessel 1, a graphite crucible 4 with a height of 100 mm and an inner diameter of 50 mm is arranged on a support 2, which is closed with a plate-shaped cover 5 in such a way that gas present in the quartz vessel 1 can enter. A graphite tube 6 is fitted in the cover 5, through which temperature control can be carried out with the aid of an optical pyrometer. The vessel 4 is surrounded by a layer J of heat-insulating graphite felt. An induction coil 8 is attached around the quartz vessel 1 for heating the device. The lid 5 is used as a substrate for depositing the crystals.

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1867657

Fig. 2 shows, in part, a different guide for this device. In the crucible 4 dsr Fig. List "uf & lmv Atoistütsung 9, a substrate 10 disposed on the. the crystals upright instead of SiüftgöiMlc as in the arrangement moh Fig. I, can grow on . Ir. FiS. 1 »Kit elsei? Fl & tte 5 covered.

The sheet 5 of FIG. 1 consists of hexagonal Sllialunkarbldkriatallen and is obtained by sublimation on a graphite plate at 2600 ° C. The plate 5 is rubbed in old iron powder with a grain size of about 5 μm. Silicon oxide is attached to the crucible 4, the bit of the carbon in the crucible 4 reacts when heated in a hydrogen atmosphere maintained in the quartz glass 1, with an oil- and carbon-containing vapor being developed. By absorbing this Daapfes in the melting iron grains and by depositing silicon carbide from the melt on the substrate 5, wire-shaped crystals grow hanging on the substrate, which often still carry an iron ball at their free end. On heating the crucible to a temperature of 1280 ⁰ C by means of the induction coil 8 an average thickness of 10 microns and a length in this way were in 65 hours, "whisker ¹ * ■ it formed to 6 ca.

Example 2

An aluminum oxide substrate is sprinkled with iron powder with a grain size of about 250 μm and arranged in the crucible 4 in the position indicated in FIG. In the crucible 4 of silicon oxide is applied which reacts with the carbon of the crucible in a quartz vessel 1 maintained in CtasatmosphMre upon heating, whereby a silicon carbon-containing ·· and steam is developed. By absorbing this vapor into the

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iron grains that melt in the process and, as a result of the deposition of silicon carbide from the aisle on the substrate 10, grow wire-like crystals on this substrate. When the crucible 4 is heated to a temperature ¹ of 120 ° O, crystals with an average length of 1 / on 3 mas and a thickness of about 200 μm are formed in 60 hours.

Example ?

A graphite residue is rubbed with iron powder with a grain size of 5M. The substrate is placed on the catfish shown in FIG. 5 used for the crucible · Zn Ti # gel 4 wi2 * d silicon attached and the device is filled with hydrogen at atmospheric pressure. When heated to 1300 ⁰ C by a VLS-grown Meohanlsmus in 50 hours on the substrate * whi3ker ^w -like Siliziuakarbldkristalle era with a length up to 2 and a thickness of 5-10 Jim.

example k

As shown in section in FIG. 3 of the drawing, whiskers 11 obtained according to Example 1 are arranged in parallel up to a height of 1 mm in a carbon die 12 which has the following internal dimensions: length 6 cm, width 2 cm and height 1 cm. the die is filled to half at a temperature of 700 ⁰ C with aluminum. After cooling, the resulting block is aue the die removed and rolled in a direction perpendicular to the longitudinal direction of the "whiskers" direction to a film having a thickness of 100 mm . the resulting film has in the longitudinal direction of the whisker * ¹ * a considerably large "tensile strength obtained as a same catfish, but without the addition of" whiskers "film.

• 10 -

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Example 5

Fig. 4 shows in Sehnitt a filter plattenfönsige filter eats "us a PIacinscMIe 13 constructed whose bottom is provided with Qttmmgßin 14" on a * m soil · "ine layer obtained according to example 3 ^w Wiigk * rs ^H 15 in any Directions in a thickness of 2 meters

The obtained chemical resistance is suitable for the chemical resistance Filter sis Filtration very sgc; ms9iver Flüselglceiten and 0 »« e.

line Vorriehtiuig according to Fig. 1 is used, the substrate 5 consists of ixagonal silicon carbide crystals. The substrate is obtained in the manner described in Example 1.

The plate 5 is rubbed in old powder of an alloy of iron and 10% aluminum with an average grain size of 5 μα. In the crucible 4 silicon oxide is attached, which reacts with the charcoal of the crucible in a hydrogen atmosphere maintained in the quartz vessel 1 when heated, whereby a silicon and carbon-containing vapor is developed. This steam is then absorbed into the core of the iron-aluminum alloy, which melts in the process. From this melt, when heated with the aid of the induction coil 8 to a temperature of 1250 ^° C., wire-shaped silicon carbide crystals with a thickness of about 10 μm are deposited on the substrate. The p-type crystals formed contain 10 ¹⁹ aluminum atoms per cm. If the aqueous atmosphere is replaced by ammonia, η-conductive silicon carbide is deposited.

If the hydrogen is replaced by ammonia for one hour every four hours, "whis-

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1667857

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If necessary, all "whiskers" are used in these cases curved! State to be completed »

Patent claims

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Claims (8)

Pat tans prltche 1. Process for the production of wire-shaped silicon carbide crystals in which the silicon carbide consists of a silicon and carbon-containing gas phase by a VLS-Mechaniw & üs on elnea substrate aiwlichatj. using a substrate having a solvent on its surface for SlllziuB and carbon that for the VLS mechanism is suitable in such a form that at elevated temperatures in the silicon and carbon containing Oasphase finely divided droplets are formed from the solvent, Silislua and carbon, by means of which Droplets of carbon and silicon from the oasis phase in Fora of monocrystalline silicon carbide precipitates in the solid-liquid orenze, characterized in that iron is used as solvent and the substrate surface provided with Elsen at temperatures of at least 1150 ° C, preferably above 1200 ° C, but generally not higher than I ¹ 100 ⁰ C, the silicon and carbon containing oasphase is exposed. 2. The method according to claim 1, characterized in that the substrate surface is previously charged with powder containing Elsen. 3. The method according to claim 1 or 2, characterized in that the silicon and carbon-containing oasis phase is produced with the aid of silicon oxide and carbon. 4. The method according to claim 3, characterized in that the silicon and carbon-containing oasis phase is produced using a hydrogen atmosphere. - 1 3 - 3 de « 209812/1250 5. Wire-shaped crystals obtained by the method according to one of claims 1 to 4. 6. Objects "especially filters" made of crystals according to claim 5 exist. 7. Objects made of plastic, glass or metal, are included in the crystals according to claim 5. 8. Semiconductor devices with silicon carbide crystals according to claim 5- Blank page